Selection pressures and sliding window analyses of the three diplozoid mitogenomes. a Sliding window analysis of the alignment of complete mtDNAs of the three diplozoids. trnG was removed from the analysis due to its position change. The black line represents the value of nucleotide diversity in a sliding window analysis (window size = 200 bp, step size = 20 bp, with the value inserted at its mid-point). Gene boundaries are indicated with a variation ratio per gene (above each gene). b Ratios of non-synonymous (dN) to synonymous (dS) substitution rates calculated from individual protein-coding genes of Paradiplozoon opsariichthydis, Sindiplozoon sp. and Eudiplozoon sp.